. Introduction to inorganic chemistry . way from the metaland up into the globe above, sothat the action ceases. Yet theaction is ready to begin p,gain themoment any portion of the storedgas is drawn off for rather sharp line can be drawn between those metals which dis-place hydcogen from dilute acids and those which, like mercury,silver, and gold, do not (see Electromotive series of the metals). Contact of the zinc or iron with an inactive metal, like platinum,always hastens the interaction, and_ therefore renders the evolution ofthe hydrogen more conspicuous. Such an arrangement is cal
. Introduction to inorganic chemistry . way from the metaland up into the globe above, sothat the action ceases. Yet theaction is ready to begin p,gain themoment any portion of the storedgas is drawn off for rather sharp line can be drawn between those metals which dis-place hydcogen from dilute acids and those which, like mercury,silver, and gold, do not (see Electromotive series of the metals). Contact of the zinc or iron with an inactive metal, like platinum,always hastens the interaction, and_ therefore renders the evolution ofthe hydrogen more conspicuous. Such an arrangement is called acouple, and its efficiency depends on the electric states of the twometals (see Solution tension). When water is not used along with the acid, the latter is eitherinactive or undergoes a different sort of chemical change. Thus, dry,gaseous or liquefied hydrogen chloride hardly interacts at all withzinc. Pure, concentrated sulphuric acid, on the other hand, althoughalmost unaffected by zinc in the cold, is violently decomposed when. Fig. 32. HYDROGEN 97 heated. The action, however, fs not a simple displacement (see below)of the hydrogen. The oxygen is removed from a part of the acid, andwater and hydrogen sulphide are formed: 4Zn + SH^SO, -♦ 4ZnS0, + ^H^O + 11,8. Preparation of Hydrogen from Water. — Every one of themetals which act on dilute acids will also displace hydrogen fromwater, and no others will do so. Onlythe more active metals, like potassiumand sodium, which would act withuncontrollable vigor on dilute acids,can displace the hydrogen rapidlyfrom cold water. Magnesium and zincshow obvious action on water at 100°only, and are much-assisted by contactwith another metal. If any action isto be perceived in the cold, the iron,nickel, zinc, and magnesium have to beused in a state of fine powder, withgreat surface. In all cases in which cold or boil-ing water is employed, the hydrogenof the water is not completely dis-placed. The metal forms an hydrox-ide, such as
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